Automatic switching device



Dec. 16, 1941. A. E. BAAK AUTOMATIC SWITCHING DEVICE Filed Aug. 4, 1939 3 Sheets-Sheet 1 on w: .w:

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AUTQMATIC SWITCHING DEVICE Filed Aug. 4, 1939 5 Sheets-Sheet 2 H3 FY1906 4--llo Ill I inventor attorney Alba-11911: 1111. Bum

Dec. 16, 1941. A. E. BAAK 2,266,144

AUTOMATIC SWITCHING DEVICE Filed Aug. 4, 1939 3 Sheets-$heet 3 w cu-r OFF 2'5 W f l CUT-OFF CUT-ON \60 2.05 ms CUT-ON CUT-OF CUT-OFF 5 ADJ- 2? ADJ.

FAN l CONTROL 2'12 '(Iiforngg Patented Dec. 16, 1941 AUTOMATIC SWITCHING DEVICE Albert E. Baak, Minneapolis, Minn., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application August 4, 1939, Serial No. 288,254

11 Claims.

This invention relates to switching devices in which a plurality of switches are actuated by a single condition responsive device.

It is an object of the present invention to provide these switches with individual adjustments whereby the condition value at which each is operated may be independently varied.

A further object is to provide a switching unit which can be used as a combination high and low limit control in connection with a temperature changing system, In this unit individual adjustments are provided for the high and low limits. The low limit control comprises a pair of sequentially operating switches, both of which must be closed to render the control operative and both of which must be opened to render it inoperative. It is also an object of the invention to provide one of these switches with a further adjustment in addition to the main adjustment. The high limit control is identical to the low limit control but operates at a different condition value due to the two main adjustments.

Another object appears in connection with the combination high and low limit control when used on a summer-winter heating system and y when operated by means of a thermostat placed in the boiler. The adjusting means for the high limit switches is provided with two indicating scales, one calibrated in temperature degrees when used in a hot water heating system, and

one calibrated in pounds when used in a steam heating system. The same thermostat is used in each case. The low limit is calibrated in degrees only, because it operates always at temperatures below that at which water boils.

Another object of the invention is to provide a floating lever which is operatively engaged by .a condition responsive element at a mid point,

and to oppose movement of the lever by spring means connected to each end of the lever whereby first one end and then the other end of the lever is moved by the condition responsive element depending upon the adjustment of each spring.

. 4 Another object is to provide a unit of the above:

Figure 2 is a side elevation looking from the right of Figure 1;

Figure 3 is a front elevation of the form shown in Figure 1;

Figure 4 is a section taken along the lines 4-4 of Figure 1 and looking in the direction of the arrows;

Figure 5 is a View of the bottom of the device showing the wiring connections;

Figure 6 is a schematic wiring diagram showing how my invention maybe used as a combination high and low limit control for a heating system;

Figure 7 shows a relay panel on which the control device illustrated in Figures 1 to 5 is adapted to be mounted;

Figure 8 is an adjustment indicating panel for a modified form of my invention;

Figure 9 is a view of the adjusting gears with the cover removed;

Figure 10 is a detailed view of the adjusting gears, and

Figure 11 is a schematic wiring diagram showing how the modified form of my invention may be used as a combination fan and high limit control.

Referring to Figures 1 to 4, reference 'numeral It] indicates an insulating base which supports the switching device of my invention. Mounted on the base I0 is a supporting member generally indicated at H which comprises four legs l2, I3, l4, and I5 and an integral connecting portion IS. The legs l2 and I4 are connected to the base by means of screws ll and legs I3 and I5 are provided with projections which extend through holes in the base in order to properly position them. (See Figure 5.) Indicated at is the main adjusting lever having one end 2| which is provided with a pair of ears operating between stops 22 and 23 on the legs I4 and 15. The other end 24 of the lever 20 is provided with a pair of cars operating between the stops 25 and 26 on the legs l2 and I3. Pivotally mounted between legs I2 and I3 as indicated at 28 is a link 5 29 which is also pivoted to the lever 20 at its mid portion as shown at 30. The purpose of this link is to prevent lateral or longitudinal movement of the lever with respect to the support I l. A pair of adjusting nuts 3| and 32 are provided, with stem portions 33 which extend through the holes 34 in the connecting portion [5 of the supporting member ll. Shoulder portions 35 are provided for supporting the nuts as shown. These nuts are internally threaded for the purpose oi adjustably supporting screws 36 Screws plate 43 having a hole therethrough to accommodate the looped end 44 of the adjusting spring 39. In this manner, the spring 39 through its engagement with the insulating member 43 normally holds the end 2| of the lever 20 against the stops 22. End 24 of lever 20 carries an insulating plate similar to the plate 43 and having a hole for accommodating the hooked end 46 of the adjusting spring 48. Spring 40 normally holds the end 24 of the lever 28 against the stops 25. I

The screws 36 are each provided with a rigidly attached arm 48 having a projecting portion 49 (see Figure 2) which extends through slots (not shown) in the legs I2 and H. The purpose of this arrangement is to prevent the rotation of the screws 36 when the nuts 3| and 32 are rotated. The shoulder portion of the nut 32 is provided with a center hole in which isinserted a hub 59 having a rigidly connected scale plate' 5|. The hub 50 and scale plate 5| are rotatably adjustable with respect to the nut 32 by means of the screw 52 which is positioned in a tapped hole in the shoulder portion 35 and which engages the hub 58. Scale plate 53 and hub 54 are adjustably positioned on the shoulder portion 35 of the nut 3| in the same manner.

From the above description, it will be obvious that rotation of scale plate 5| and nut 32 will vertically adjust the nut 38 and hence vary the tension of the spring 40, and in a like manner rotation of the scale plate 53 will adjust the tension of the spring 39.

The four legs l2, |3, l4 and I5 are adapted to support the plate.56 which carries a bellows 51. Capillary tube 58 connects the bellows 51 to a thermal bulb which is placed in the area to whose temperature it is .desired that the bellows respond. It is ObViOlls that the bellows 51, could be made to respond to pressure instead of temperature if desired. The lower end of the bellows is provided with a point 60 which seats in the bearing member 6| carried by the lever 29.

Expansion of the bellows will therefore have the effect of pushing the lever 20 in a downwardly direction as seen in Figures 2, 3, and 4.

The insulating base I9 is provided with a pair of projections 63 and 64 whose upper ends are connected by means of a metallic plate 65. (See Figure 2.) Adjustably positioned in the plate 65 are a pair of stationary contacts 66 and 61. The contact 61 projects slightly lower than the contact 66 for a purpose which will appear hereinafter. The insulating base III is provided with a second pair of projections 68 and 69 at the other end of the supporting member. Metallic member I8 carried by projection 68 adjustably positions the stationary contact I and metallic member 12 carried by the projection 69 adjustably positions the contact I3. The contact 13 extends slightly lower than the contact II for a purpose which will appear later.

The insulating base III also carries a center projection 15 on which is positioned a resilient 7|. Placed alongside of the contact blade 16 on the projection 15 is a second contact blade 19, one end of which is reinforced by a stiff blade 83 which carries contact 8| which cooperates with the stationary contact 61. The other end of the blade 19 carries a reinforcing blade 82 which carries a contact 83 which cooperates with the stationary contact 13.

Adjusting arm 85 is provided with projections 86 which ride in the slot 81 in arm I3. A screw having a knurled head 88 screw-threadedly engages the arm 85 to tighten it in the slot-.81 and thereby hold it in any desired adjusted position therein. The inner end of the arm 85 is provided with a hole 90 in which is hooked one end of an adjustment spring 9|. The other end of the spring 9| supports a link 92 which engages the hooked end 93 of the stifi blade 89. The link 92 has been broken away in Figure 2 in order to show. the contact structure more clearly. The effect of the spring 9| is to normally hold the contact 8| in engagement with contact 61 and the force with which these contacts are held in engagement is adjustable by means of the arm 85 in the slot 81. Likewise, the arm 94 is adjustable in slot 95. by means of the screw 96. Arm 94 carries the adjustment spring 91 which through the link 98 engages the blade 82 to hold contact 83 into engagement with the contact 13. Spring 91 is adjustable in the same manner as spring 9|.

Bracket 99 carried on the connecting portion |6 of the supporting member carries the screws I00 and I55 and clamps |0| which clamp the scale plates 5| and 53 to prevent their accidental displacement after they have once been moved to their adjusted positions. It is noted that the scale plate 5| carrie markings which represent temperatures in degrees Fahrenheit and that the scale plate 53 carries two sets of markings, one set being in degrees Fahrenheit and the other set being in pounds pressure. The purpose of the two scales on the plate 53 will appear in the description of the system in which the switching mechanism is adapted to be used.

Figures 1 to 4 disclose the parts in the positions that they will occupy when the temperature to which the bellows 51 responds is at a low value. It will be understood that the spring 49 will be adjusted so that the end 24 of the lever 20 will be actuated at one temperature and f As the temperature to which the bellows responds increases to a value of the bellows will start to' expand and due to the adjustments of the scale plates 5 and 53, the spring 39 will oppose this expansion with a greater force than the spring 40. Due to this fact the end 24 of the lever 20 will first start to move in a downwardly direction. After it has moved a slight distance, it will first engage the spring blade 16 to move the contact out of engagement with the stationary contact 66. This is due to the fact that the contact 66 does not extend down as far as the contact 61. On a very slight additional movement of the end 24 of the lever- 20, the in sulating plate 45 will engage the stiff blade 80. As movement of the member 80 is resisted additionally by the spring 9|, the lever 20 will remain stationary until the temperature to which the blades H2 and H3. ranged that on a decrease in temperature the bellows responds has risen sufllciently for the bellows 51 to develop an additional force to overcome the tension of this spring. At this time the bellows will again expand and separate th contact 8I from the stationary contact 61. A slight additional movement of the lever 20 will cause the end 24 to engage the stop 26 and prevent its further movement. The lever 20 will remain in this position until the temperature rises to 180 indicated on scale plate 53, at which time the bellows 51 will exert sufllcient force to overcome spring 39 and move the end 2| of the lever 20 out of engagement with the stops 22 causing the insulating plate 43 to engage the spring blade I6 and separate the contact I8 from the contact II. As contact 13 extends lower than contact II it will require a slight additional movement of the bellows to cause the Plate 43 to engage member 82 whose movement is additionally opposed by the tension spring 91. .The lever 20 will therefore not move further until bellows 51 has developed sufficient force, due to a further increase in temperature, to overcome the tension of the spring 91 at which time the plate 43 willl move the contact 83 out of engagement with contact I3. A slight additional expansion of the bellows will cause the end 2I -of the lever 20 to engage the stops 23 after which no additional downward movement of the lever 20 can take place.

On a decrease in the temperature to which the bellows responds the bellows will contract causing contacts 83, 18, 8|, and 11 to engage their respective stationary contacts in the order named. It will be seen therefore that this mechanism provides for one adjustment for determining the temperature value at which one pair of switchesis actuated and a second adjustment for determining the temperature value at which the second pair of switches is actuated. Furthermore, the springs 9I and 91 provide for the individual adjustment of the differential between each pair of switches.

Figure 6 illustrates diagrammatically a heating system in which the above mechanism may be advantageously used. The insulating panel I has been shown in dotted lines in this figure whichalso shows the bellows 51, main adjusting springs 39 and 40, contact blades I6 and I9 as well as the various movable and stationary contacts. It will be appreciated that the insulating plates 43 and 45 have been shown as comprising two separate legs merely for the sake of clarity and convenience. The room thermostat indicated generally at H0 comprises a bimetallic coil III which is fixed at one end and which carries at its free end a pair of contact These blades are so arupon energization is adapted to pull in the switch blades I22 and I23 to engage the contacts I24 and I25, respectively. A temperature changing device such as an oil burner motor is indicated the boiler of the furnace heated by the temperature changing device I26.

With the parts in the positions shown in Figure 6, the boiler water temperature will be between and because the end 24 of lever 20 has opened its switches whereas the end 2| of the lever 20 is permitting its switches to remain closed. The room thermostat H0 is shown as being satisfied and the burner motor I26 is therefore deenergized. On a decrease in room temperature the resilient blade H3 will first engage the stationary contact H4 but no circuit will be established at this time due to the fact that the switch blade I22 is in open position and the switch blaile I I2 has not yet engaged the contact H5. On" a further decrease in room temperature, the switch blade H2 will engage the stationary contact H5 and establish the following circuit: secondary winding I20, conductor I30, terminal I45, conductor I46, stationary contact I3, contact 83, switch blade 19, conductor I3I, terminal I32 on the insulating base I0, conductor I33, contact H4, switch blades H3 and H2, contact H5, conductor I34, terminal I35 on insulating base I0, conductorl36, switch blade I6, contact 18, contact II, conductor I3I, terminal I38 on insulating base I0, conductor I39, relay winding IN; and conductor I40 back to the secondary I20. This circuit energizesthe relay winding I2I causing'the switch blades I22 and I23 to engage their respective contacts l24 and I25. The engagement of the blade I23 with contact I25 energizes the' burnermotor I26 by means of the terminal I48 on the insulating base I0, conductor the switch blade H3 disengages the contact H4.

Assuming that the room thermostat H0 continues to call for heat, the boiler water temperature will increase and after it reaches a temperature of 180", as set on the scale plate 53, the bellows 51 will begin to expand first disengaging the contacts II and I8. Disengagement of these contacts will have no effect upon the system due to the fact that the holding circuit traced above does not pass throughthese contacts. Further expansion of the bellows 51 will disengage the contacts I3 and 83 which will break the above traced circuits and deenergize the relay winding I 2|. This will result in deenergizing the burner motor I26 and the boiler water temperature will therefore begin to decrease. Reengagement of the contacts 83 and I3 will not reenergize the relay winding I2I at this time because the original energizing circuit for the relay must pass through the contacts II and 18 due to the fact that the holding contacts I22 and I24 are open. After at I26 but it will be appreciated that any other type of heating device may be substituted therefor. In this case the capillary 58 connects the bellows 51 to a thermal bulb which is placed in the boiler water temperature has decreased to a point where the bellows 5I reengages the contacts II and I8, the relay winding I2I will be reenergized providing the switch blades II 3 and H2 are engaging the stationary contacts H4 and iii. In other words, the energizing circuit for the relay I2I must pass through contacts 33 and 13, H4 and H3, H2 and III, and also 1I and 13. After the relay has been pulled in, the holding circuit includes the contacts 33 and 13, H4 and H3, and I22 and I24.

If the room thermostat IIO remains satisfied for a suilicient length or time, the boiler water temperature will decrease to slightly below I50, at which time the bellows will contract to cause the contacts 3i and 51 to engage. Engagement of these contacts will not affect the system due to the fact that the circuit to the secondary winding I must pass through the contacts 55 and 11. On further decrease in boiler temperature, the contacts 55 and '11 will be engaged at which time the relay winding I2I will be energized by the following circuit: secondary I 20, conductor I30, terminal I45, conductor I45, contacts 13 and 33, contact blade 13, contacts 3i and 51, conductors I52 and I53, contacts 11 and 55, switch blade 13, contacts 13 and H, conductor I31, terminal I33, conductor I33, relay winding I2I, and conductor I40 back to the other side of the secondary I20. Energization of the relay I2I will energize the burner motor I and will close the holding contacts I22 and I24 which establishes a holding circuit for the relay winding I2I independently of the contacts 55 and 11. This circuit goes from the secondary I20, conductors I and I43, contacts 13 and 33, switch blade 13, contacts and 3i, conductors I52, I54, and I43, contacts I24 and I22, conductor I50, relay winding I2I, and conductor I back to the secondary winding I20. It will therefore be seen that to energize the relay windfng I2I by the limit switches actuated by the bellows 51, that all four of these switches must be in closed position and that in order to break the circuit to the relay winding I2I the contacts 3| and 51 in addition to contacts 33 and 11 must be opened. In other words, the relay will be pulled in at one temperature and will be broken at a higher temperature thereby establishing a definite diilerential oi operation. It will be noted also that a differential of operation .is established by the high limit switches 13 and 33 and 13 and H and also by the room thermostat with its two sequentially operating switch blades ,I I3 and H2. The result of this operation is that the burner motor can never be operated on and oil rapidly, but after it has once been turned on it must remain on until the temperature of the boiler water or the temperature in the room has been raised a predetermined amount, and after it has been deenergized either by the limit switch or by the room thermostat it must remain deenergized until the boiler water has decreased in temperature or the room has decreased in temperature a predetermined amount.

In the above description of operation, it has been assumed that the control is placed on a hot water heating system in which the high limit switch operates at 180. This same control device may also be used in connection with a steam heating system. In this case, the limit switch will be actuated at a higher temperature which will be above 212 and somewhere in the steam range. In order to adapt the control device for such use, the adjusting dial 53 must be rotated in a direction to increase the tension of the spring 33 and to place the scale which is callbrated in pounds pressure adjacent the indicat ing means. In the first place, attention is called to the fact that the screw I limits the rotation of the scale plate 53 in its adjustment over the range from to In order to change to the pressure scale, the screw I55 is loosened and moved to the right in its slot I55, at which time the shoulder I51 on the plate 53 may pass by the screw I55 so that the plate may be rotated in a clockwise direction until the pressure scale is opposite the screw. When the proper adjustment on the pressure scale has been made, the screw I55 is again moved to the left and tightened to clamp the plate 53 in its'adjusted position. In order that the plate 53 cannot be rotated in the wrong direction to change over from the temperature to the pressure scale, the projection I53 is made sufl'iciently long so that it cannot pass the screw I55 even' after it has been retracted in the slot I56. In other words, to change from the temperature to the pressure scale, the plate 53 must be rotated in a clockwise direction and to change from the pressure to the temperature scale it must be rotated in a counterclockwise direction. The scale plate 5I is calibrated in degrees only because the low limit switch is to be operated at a temperature well below that of the boiling point of water regardless of whether the control device is used on a hot water or a steam heating system.

In Figure 7, a relay panel I50 is shown as supporting the transformer I I 9 and the relay I2I. The terminal I33, I45, and I43 are disclosed and as seen in connection with the schematic diagram of Figure 6 wires I34, I33, and I41 may be connected thereto in the order named if it is desired that the burner motor I25 be controlled by the room thermostat only. It is one of the primary objects of the present invention to design this combination high and low limit control so that it may be integrally mounted on the relay panel I50 in the simplest manner possible. In order to insert this limit control into the circuits, it is necessary merely to remove the terminal screws I45 and I43 and disconnect all three of the wires I34, I33, and -I41. It will be noted that the screw I45 is permanently mounted in a recess in the insulating panel I0 by means of the plate I53 connected to the bottom of the base I0 as seen in Figure 5. A spring contact member I33 15 also supported on the bottom of the base by means 01' the rivet I 31. The control device is placed on the panel I50 so that the spring blade I33 makes contact with the terminal screw I33 on the panel I50. The screw I45 which is permanently mounted in the base I0 is screwed into the panel I50. The terminal screw I43 is inserted through the hole I48" in the base I0 and screwed into the panel I50. These two screws I45 and I43 serve to mount the control device on the panel I50 and maintainthe spring blade I33 in engagement with the terminal screw I33. The room thermostat H0 is now connected to the control device by connecting wire I41 to the terminal I43, wire I33 to the terminal screw I32 mounted on base l0 and wire I34 to terminal screw I 35 also mounted on base I0. The control device is internally wired so that these are the only connections necessary to properly insert this device in the circuit. Comparing Figures 5 and 6, it will be seen that the rivet I31 in Figure 5 connects spring I33 to member 10 and contact 1| in Figure 4 and corresponds to conductor I31 in Figure 6 and that the rivet I45 connects screw I45 and plate I 53 to member 12 and contact 13 in Figure 3 and corresponds to the conductor I45. Likewise, the conductors I3I, I35, and I54 in Figure 5 correspond to these same conductors in Figure 6. The rivet I3I shown in Figure 5 connects conductor I3I with the spring blade 18 and the rivet I36 in Figure 5 connects conductor I36 with the spring blade 16 shown in Figure 4. Therefore the only operations required to insert this control device into the control circuit is to remove the terminal screws I45 and I48 in the panel I60 and use them to support the base I0 on the panel I60 and then wire the thermostat to the terminals I48, I32, and I35 on the base I0.

Another use to which this control device may be put is to act as a combination high limit and fan control for a hot air heating system. Such a system has been shown diagrammatically in Figure 11. In view of the fact that the range between thehighest temperature to which the limit switch may be adjusted and the lowest temperature to which the fan switch may be adjusted is too large to be properly handled by a single temperature responsive bellows, two separate control units are provided, each of which is actuated by a separate bellows. As in the case of the combination high' and low limit control, it is necessary to actuate only four switches and as two separate levers are actuated by the bellows eachend of each lever actuates a single switch instead of the two switches where only a single lever is used. Inasmuch as the two switches of each device are used in combination with a relay and holding circuit as described above, the movement of one end of the lever controls the temperature at which the relay is pulled in and movement of the other end of the lever controls the temperature at which the relay is dropped out. These temperatures are individually adjustable by means of the two springs and in order to prevent the springs from being so adjusted that the sequence of switch operation is changed, some sort of an interlock between the adjusting devices is necessary. Such an interlock is disclosed in Figures 9 and 10.

Referring to Figure 10, the reference numeral 200 indicates the connecting portion of a supporting member similar to supporting member 'II of Figures 1 to 4. Two adjusting nuts are provided at 20I and 202 for adjustingthe springs (not shown) which determine the operation of the switching device. The nut 20I has an upwardly projecting stem 203 which is provided with a kerf so that the nut :01 may be rotated in 5 order to adjust its spring. The supporting member 200 is provided with an axle 204 between the two adjusting nuts on which there is concentrically mounted a pair of gears 205 and 206. The pinion gear 201 is mounted on the stem 203 and as this stem is rotated to adjust the nut 20I, the

gear 201 meshes with the gear 206 to rotatably position it on its axle. In like manner, when the stem 208 on nut 202 is rotated the pinion gear 209 meshes with the gear 205 to position it in accordance with the adjustment of the nut 202. As seen in Figure 9, the gear 206 is provided with indicia which cooperate with an in-w dicator (Figure 8) to indicate the adjustment of the nut 20I. The gear 206 is also provided with an arcuate slot 2I0 through which is visible at scale 2I I on the gear 205. The gear 205 is provided with a pin 2I2 which projects through the slot 2I0 to limit the relative rotation between the two scales. This limits the relative adjustments of the nuts 20I and 202 so that one of the adjustment springs must always exert the greater force and therefore one of the switches actuated by this device must always be closed before the other switch. A cover plate 2I5 is carried by the supporting member 200 by means of screws 2I6.

The two control devices are located side by side and each is provided with the adjusting device just described. The cover 2I5 'is large enough to cover both of these devices and is provided with holes 2 I 1 through which the stems on the adjusting nuts project. It will be noted with reference to Figure 8 that the cover plate 2I5 indicates which is the high limit and which is the fan control and also which scale indicates the cut-off temperature and which the cut-on temperature. There is also an indication adjacent each of the steps of the adjusting nuts as to which limit that particular stem is adapted to adjust.

Referring now to Figure 11, the room thermostat 220 is shown as being comprised of a bimetallic coil 22I which is fixed at one end and carries at its free end a pair of switch arms 222 and 223 which on a fall in temperature engage stationary contacts 224 and 225 in the order named. The high limit control comprises a bellows 221 which is connected by means of a capillary tube 228 to a thermal bulb 229 located in the bonnet of the furnace 230. The bellows 221 actuates the floating lever 23I having insulated ends 232 and 233. Movement of the lever 23I by the bellows 221 is opposed by means of the springs 234 and 235. It will be understood that the bellows, lever, and adjusting springs are substantially the same as described in connection with Figures 1 to 4.

Bellows 236 is connected by means of the capillary 231 to the thermal bulb 238 located in the bonnet of the furnace. This bellows actuates a floating lever 239 against the force exerted by springs 240 and 24I. The usual oil burner or other heating device is shown at 242 and a fan 243 is provided for forcing the air through the furnace and into the rooms to be heated. The electric power for the control system is supplied from the lines 244 and 245 to the primary winding 246 of the step-down transformer 241.

Assuming that the air in the bonnet of the furnace is relatively cool, the bellows 221, which acts as the high limit control, will be contracted so that switch arms 232 and 233 will be in engagement with the stationary contacts 250 and 25I. The bellows 236, which controls the fan, will also be contracted so that the switch arm 239 is out of engagement with contacts 252 and 253. On a decrease in room temperature the bimetallic element 22I of the room thermostat 220 will move the flexible contact arm 222 into engagement with its stationary contact 224. The closure of this switch will have no efl'ect on the circuit. On a further decrease in temperature the switch arm 223 will be moved into engagement with its stationary contact 225 at which time the following circuit will be established: from the secondary winding 255 of the trans former 241, conductors 256, 251, contact 250, switch arm 232, conductor 256, contact 224, contact arms 222 and 223, contact 225, conductor 250, switch arm 233, contact 25I, conductor 260, relay winding 26I, and conductor 262 back to the secondary 255. This will energize the relay winding 26I and pull in the switch arms 262 and 263 which will cause them to engage contacts 265 and 266, respectively. The engagement of switch arm 262 with contact 265 will set up a holding circuit for the relay winding 26I independently of the switch arm 223, and contact 225. This circuit extends from conductor 258, contact 224, switch arm 222, bimetallic element 22 I, conductor great.

261, contact 265, switch arm 262, and conductor 268 to the relay coil 26L Engagement 01' the switch arm 263 with the contact 266 establishes a. circuit from the line wire 218, switch arm 263, contact 266, conductor 2", and burner motor 242 back to the other line wire 212. This results in energizing the burner motor 242 which increases the temperature of the air within the bonnet of the furnace. An increase in this air temperature to 120, as set on the scale in Figure 8, causes an expansion of the bellows 236 which first causes the contact blade 239 to engage the stationary contact 252. Closure of these contacts does not affect the circuits. On further increase in air temperature to 140 the bellows 236 causes the switch blade 239 to engage stationary contact 253 which establishes the following circuit: from secondary winding 255, conductors 256 and 214, contact 252, witch blade 239, contact 253, conductor 215, relay winding 216 and conductor 211 back to the secondary 255. This energizes the relay winding 216 which causes the switch arms 218 and 219 to engage stationary contacts 288 and 281, respectively. Engagement of the switch arm 218 with contact 288 sets up a holding circuit for the relay winding 216 independently of the stationary contact 253. This circuit extends from conductor 214, contact 252, switch blade 239, conductor 282, contact 288, switch arm 218, and conductor 283 to'the relay winding 216. The relay winding 216 will therefore remain energized until the contact blade 239 separates from the stationary contact 252.

The energization of the relay winding 216 also causes the switch arm 219 to engage the contact 28! which sets up a circuit from the line wire 285 to contact 28|,switch arm 219, conductor 286, and fan motor 243 back to line wire 281. The system is now. operative to deliver hot air to the various rooms to be heated. This action will continue until the room thermostat 228 causes both switch arms 222 and 223 to separate from contacts 224 and 225. If the room thermostat 228 should continue to call for heat until the air temperature in the bonnet of the furnace reached 180, as set on the high limit scale in Figure 8, bellows 221 would expand and move switch arm 233 out of engagement with contact 251. This would have no effect upon the system due to the holding circuit for relay winding 26!. It the bonnet temperature increased to 220 bellows 221 would move arm 232 out of engagement with contact 258 and deenergize relay winding 26l thereby deenergizing the burner motor 242. After the burner motor 212 has once become deenergized due to the dropping out of the relay 26l, it cannot be reenergized until the high limit bellows closes both of its switches and the room thermostat 228 closes both of its switches. It is clear of course that after the burner motor has been deenergized, the fan will continue to run until the temperature of the air in the bonnet is decreased to a point where the bellows 236 causes the switch blade 239 to disengage both contacts 252 and 253.

It will be appreciated that the switching devices used in the combination Ian and high limit control are substantially the same as those used in the combination high and low limit control and that the only reason a single bellows is not used is because the temperature range is too Also, whereas in the combination high and low limit devices one end of the lever actuates both of the high limit switches, in the fan and high limit control devices one end 0|. the lever actuates one of the high limit switches and the other end of the lever actuates the other of the high limit switches. In every case, however, the arrangement of the bellows, the main adjusting lever and the two adjusting springs for the lever remain the same.

As other changes and modifications in this invention may occur to those skilled in the art, I wish to point out that I am to be limited by the scope of the appended claims rather than by the specific embodiments of the invention disclosed herein.

I claim as my invention:

1. A control device comprising in combination, an actuating member, a condition responsive device operatively engaging said member at an intermediate point, first and second means connected to said member at opposite sides of said point for resisting movement of said member by said condition responsive device, means for individually adjusting said means, and control devices actuated respectively by opposite ends of said member.

2. A control device comprising in combination, an elongated actuating member, a pair of circuit controlling means actuated selectively by the ends of said member, a condition responsive device operatively engaging said member at an intermediate point, biasing means associated with each end of said member for exerting different effects thereon whereby said circuit controlling means are actuated at different values of said condition, and means for adjusting at least one of said biasing means to vary the condition value at which the corresponding circuit controlling means is actuated.

3. A control device comprising in combination, and actuating member, a condition responsive device operatively engaging said member at an intermediate point, first and second means connected to said member at opposite sides of said point for resisting movement of said member by said condition responsive device, means for individually adjusting said means, control devices actuated respectively by opposite ends of said member, a stationary support, and a link pivotally connected to said support and said member whereby said member cannot be laterally displaced.

4. A control device comprising in combination, a floating lever, a first spring connected to one end of said lever, a second spring connected to the other end of said lever, a condition responsive device engaging said lever at an intermediate point for moving first one and then the other end of said lever against the action of said springs depending upon which spring exerts the greater force, a first switch actuated by one end of said lever, a second switch actuated by the other end of said lever, and individual adjusting means for each spring whereby the condition value at which each switch is actuated may be individually adjusted.

5. A control device comprising in combination, a. floating lever, a first spring connected to one end of said lever, a second spring connected to the other end of said lever, a condition responsive device engaging said lever at an intermediate point for moving first one and then the other end of said lever against the action of said springs depending upon which spring exerts the greater force, a first switching means actuated by one end of said lever, a second switching means actuated by the other end of said lever, each switching means comprising a first switch movable to open position by said lever, a second switch movable to open position by said lever after said first switch has been opened, and adjustable spring means opposing opening of said second switch whereby the difierential between the opening values of said first and second switches may be varied.

6. A combination high and low limit control comprising a floating lever, a first spring con nected to one end of said lever, a second spring connected to the other end of said lever, a temperature responsive bellows engaging said lever at an intermediate point for moving first one end of said lever and then the other against the action of said springs depending upon which spring exerts the greater force, a limit switch actuated by each end of said lever, individual adjusting means for each spring, and two scales operating with one of said adjusting means, one scale being calibrated in degrees for when the bellows responds to hot water temperature, the other scale being calibrated in pounds for when the bellows responds to steam pressure.

'7. A unitary high and low limit control for use in controlling the boiler temperature in a summer-winter heating system comprising in combination, a high limit switch, a low limit switch, a single thermostatic element responsive to boiler temperature for actuating both switches,

adjusting means for adjusting the temperature at which said low limit switch. is actuated, said temperature being always below the boiling point of water, a scale for indicating said adjustment in degrees, a second adjusting means for adjusting said high limit switch, said second adjusting means having two ranges, one range for use in a hot water heating system and the other range for use in a steam heating system, and a pair of scales for indicating the adjustment of said second adjusting means, one scale being calibrated in degrees for indicating the adjustment when said one range is being used, the other scale being calibrated in pounds for indicating the adjustment when said other range is being used.

8. A control device comprising in combination, a floating lever, a first spring connected to one end of said lever, a second spring connected to the other end of said lever, a condition responsive device engaging said lever at an intermediate point for moving first one and then the other end of said lever against the action of said springs depending upon which spring exerts the greater force, a pair of stops for each end of'said lever, B. first switching unit comprising a pair of stationary contacts adjacent said one end of said lever, a pair of contact blades biased into engagement with said contacts, said stationary contacts .being so adjusted that as said lever is actuated it moves first one contact blade and then the other out of engagement with its stationary contact, a

third spring connected to said other. contact blade and resisting its movement by said lever, means for adjusting said third spring whereby the condition value at which said other contact blade is moved may be varied independently of said first spring, and a second switching unit similar to said first switching unit associated with the said other end of said lever.

9. A control device comprising in combination, a floating lever, a first spring connected to one end of said lever, a second spring connected to the other end of said lever, a condition responsive device engaging said lever at an intermediate point for moving first one and then the other end of said lever against the action of said springs depending upon which spring exerts the greater force, a first switch actuated by one end of said lever, a second switch actuated by the other end of said lever, an adjusting means for said first spring, an adjusting means for said second spring, and an interlock between said adjusting means preventing them from being adjusted in a manner to change the sequence of switch operation.

10. A control device comprising in combination, a floating lever, a first spring connected to one end of said lever, a second spring connected to the other end of said lever, a condition responsive device engaging said lever at an intermediate point for moving first one and then the other end of said lever against the action of said springs depending upon which spring exerts the greater force, a first switch actuated by one end of said lever, a second switch actuated by the other end of said lever, an adjusting means for said first spring, an adjusting means for said second spring, a pair of concentrically mounted indicating members, one operated by one of said adjusting means and one operated by the other, and an interlock between said indicators to prevent the sequence of switch operation from being changed by either of said adjusting means.

11. A control device comprising in combination, a floating lever, a first spring connected to one end of said lever, a second spring connected to the other end of said lever, a condition responsive device engaging said lever at an intermediate point for moving first one and then the other end of said lever against the action of, said springs depending upon which spring exerts the greater force, a first switch actuated by one end of said lever, a second switch actuated by the other end of said lever, an adjusting means for said first spring, an adjusting means for said second spring, a pair of concentricallymounted indicating members, one operated by one of said adjusting means and one operated by the other, a slot in one member, a pin on the other member riding in said slot so as to limit the-relative adjustment of said adjusting means.

ALBERT E. BAAK. 

